Demands for miniaturization, higher density, and cost reduction of, for example, a mobile phone apparatus and a communication apparatus used for a mobile communication are being increased. The miniaturization and higher density are realized by allowing a single component to have plural functions incorporated to thereby decrease the number of components.
Electronic components used in the communication apparatus include a filter that passes a signal in a particular frequency band from an electric signal received by an antenna, an amplifier that amplifies the electric signal, and a directional coupler (coupler) that monitors an electric signal transmitted through a line.
Japanese Patent No. 5327324 describes a directional coupler including a low-pass filter. The low-pass filter is connected to a sub line electromagnetically coupled to a main line and includes a capacitor and a coil.
Various frequency bands are used for communications in communication apparatuses. Characteristics of some components mounted in such communication apparatuses may change depending on frequencies. Thus, the components mounted need to be changed for each frequency band. The directional coupler described in Japanese Patent No. 5327324 uses an LC low-pass filter including a capacitor and a coil and reduces a change, based on a frequency, of a coupler output represented by an attenuation amount of an electric signal output from the sub line to thereby realize a directional coupler that can cope with a wide frequency band.
The directional coupler described in Japanese Patent No. 5327324 can reduce a change based on a frequency of a coupler output, but an insertion loss represented by an attenuation amount of an electric signal output from the main line may change depending on frequencies.